Documents of value, sometimes referred to as security documents, such as currency, stock and bond certificates, and the like, require assessment of their genuineness and/or value recognition with certainty and rapidity. Equal importance is directed to providing means for such verification which itself is difficult to counterfeit. Detectable indicia can be applied in an encoding pattern upon the document, which indicia offer recognition of genuineness. Further, such encoding indicia permit value recognition for identification, sorting, evaluation and like purposes. Preferably, the indicia employed should be invisible to the naked eye, yet should be instantaneously apparent when detection and/or recognition is desired, preferably by one who is not skilled or sophisticated, employing easily operated, low-cost detecting and/or recognition equipment.
The indicia requirement per se may be met by applying a minute quantity of an electrically conductive medium, a metal for example, in a very thin coating uniformly in bands or other pattern over a portion of the document surface. In selecting the material comprising the indicia, and selecting the method of application, the choice should be restricted to ones which are economically and/or technically, difficult and expensive to effect so that duplication of such encodings are out of the economic reach of likely counterfeiters and the like. The encodings should be visually transparent, while retaining a clear differentiating characteristic, the presence or absence of which can be detected.
With available methods and means, detection and/or identification require sophisticated techniques and often complex sensing devices. Further, with wear, bends, creases occasioned, say with repeatedly circulated currency for example, the effective detectability of the genuineness and/or recognition of value by sensing of applied indicia is reduced markedly. It is very difficult to recognize discontinuous coatings by methods available to the art. Recognition by resistance or conductivity measurements normally requires indicia coating thicknesses that render the coatings visible, a factor that reduces their effectiveness.
In copending application Ser. No. 085,259 filed Oct. 16, 1979, owned by assignee hereof, there is described a security document which is encoded with a thin, transparent coating which is normally invisible and includes particles driven into the surface of the carrier substrate to a substantial depth. The selected coating is laid down in a limited area of the substrate surface in an encoding pattern which can be readily identified when detected. A second coating can be applied to the overall document so that all areas of the document have the same overall appearance whereby additionally to mask visible detection of the presence of such encoding indicia.
Wear, creasing, aging, discontinuities or other physical impairment of the document should not deleteriously affect the detection of the selected indicia and pattern thereof. The detecting device should be economical and preferably should be small enough to enable placement, say on a counter or the like, or upon a desk for point of sale usage, for example the device should be portable and of low cost. Additionally, it would be of considerable advantage if the operation of the detector device did not require withdrawing the subject document from visual observation during the determination of genuineness, etc.
In addition to detection and recognition, an additional function which advantageously could be effected at the same time as inspection involves the performance of a function in response to such detection and/or recognition. Accordingly, the detection or recognition device should be responsive to a particular signal to cause a secondary function such as a digital display, a comparison with a preprogrammed memory device, or produce a signal which can be directed to effect other secondary functional operations such as effecting accounting functions, and even trigger a memory device to ascertain correct record ownership of the inspected document.